|Locomotive|Named|Serial No|Entered service|Gauge|Livery|
|---|---|---|---|---|---|
|BL26|Bob Hawke|83-1010|March 1983|Standard|Pacific National blue & yellow|
|BL27||83-1011|August 1983|Standard|Pacific National blue & yellow|
|BL28||83-1012|September 1983|Standard|Pacific National blue & yellow|
|BL29||83-1013|October 1983|Broad|Pacific National blue & yellow|
|BL30||83-1014|December 1983|Standard|Pacific National blue & yellow|
|BL31||83-1015|November 1983|Standard|Pacific National blue & yellow|
|BL32||83-1016|February 1984|Broad|National Rail orange & grey|
|BL33||83-1017|April 1984|Standard|Pacific National blue & yellow|
|BL34||83-1018|June 1984|Broad|Pacific National blue & yellow|
|BL35||83-1019|July 1984|Standard|Pacific National blue & yellow|

Question: how many locomotives entered service after the bl31?
Answer: 4